An edge-light type surface light source device in which a light guide plate is employed has come into widespread use mainly as a backlight for a liquid crystal.
An edge-light type surface light source device has become prevalent in a backlight for a liquid crystal. This is because the edge-light type surface light source device is more effective in thinning (i) a backlight module for a liquid crystal and (ii) a product to which the backlight module is applied, as compared with a direct type backlight. Note that (a), in the direct type backlight, a light source is arranged directly under a liquid crystal panel instead of using a light guide plate, whereas (b), in the edge-light type surface light source device, (i) a linear light source is arranged on an edge of a light guide plate and (ii) the light guide plate converts light into plane emitting light (see, for example, Patent Literature 1). Furthermore, in some cases, the edge-light type surface light source device is employed also as an illumination.
Conventionally, a cold cathode fluorescent lamp (CCFL) has been prevalent in a light emitting source of such a light source device. Note, however, that the cold cathode fluorescent lamp (CCFL) has been recently replaced with a light emitting diode (LED). This makes it possible to (i) eliminate use of mercury, which (a) is employed in the CCFL and a fluorescent tube and (b) imposes a heavy burden on the environment, (ii) reduce power consumption, (iii) increase color reproducibility, and (iv) prolong a life of the light source device.
The following description will discuss a conventional edge-light type surface light source device with reference to FIGS. 14 through 25. FIG. 14 is an exploded perspective view illustrating a configuration of a conventional edge-light type surface light source device. FIG. 15 is a cross sectional view illustrating the conventional edge-light type surface light source device, illustrated in FIG. 14, which the conventional edge-light type surface light source device has been assembled.
An LED light source device 100, which is a conventional edge-light type surface light source device, includes a housing 160, a light guide plate 120, a reflecting sheet 130, a diffusing sheet 150, and an LED light source substrate 140 (see FIGS. 14 and 15).
In a case where a relatively thin light guide plate is used as the light guide plate 120, such a light guide plate may be referred to as a light guide sheet. Note, however, that there is no accurate difference between the light guide plate and the light guide sheet, so that these two terms have been in general use to suit the occasion. Note, under this description, that a member referred to as the light guide plate 120 is a general light guide section including a member referred to as the light guide sheet.
The LED light source substrate 140 emits light with which the light guide plate 120 is irradiated. The light emitted from the LED light source substrate 140 enters the light guide plate 120 via an incident surface which is a side surface of the light guide plate 120. Such incident light is mixed and uniformized in the light guide plate 120 so as to be surface light and then exit via a top surface of the light guide plate 120, i.e., via which the surface light exits.
The reflecting sheet 130 is arranged on a back surface side (on a side of a surface opposite to the surface via which the surface light exits) of the light guide plate 120. This causes light, which has leaked to the back surface side, to return into the light guide plate 120, so as to contribute to an increase in utilization efficiency of light.
The diffusing sheet 150 (i) is arranged on a front surface side (on a side of the surface via which the surface light exits) of the light guide plate 120 and (ii) uniformizes light which has exited via the front surface side so as to bring about an effect of reducing unevenness of luminance. The diffusing sheet 150 is used, as needed, in combination with various other optical sheets (e.g., a lens sheet, a polarization reflecting sheet, etc.).
The housing 160 (i) contains therein the aforementioned members and (ii) fixes and supports therein the members.
With the arrangement, the LED light source device 100 functions as a surface irradiation device which uses light emitted from the LED light source substrate 140.
The following description will specifically discuss, with reference to FIGS. 16 through 19, a configuration of an LED light source substrate of a conventional edge-light type surface light source device.
FIG. 16 is an external view illustrating an LED light source substrate of the conventional edge-light type surface light source device. FIG. 17 is a cross sectional view illustrating the LED light source substrate illustrated in FIG. 16.
The LED light source substrate 600 is configured such that a plurality of LED packages 620 and a connector 601 are provided on a flat wiring substrate 610 (see FIG. 16). The LED package 620 is electrically connected to an outside (not illustrated), via the connector 601 and a harness (not illustrated), so that light emitting is externally controlled.
The following description will further discuss in detail configurations of surroundings of the LED package 620 with reference to FIG. 17.
The wiring substrate 610 is configured such that a substrate 611, a wiring layer 612, and a solder resist layer 613 are laminated. The LED package 620 is connected and fixed on the wiring layer 612 via a solder 626.
The LED package 620 includes an LED element 621, a sealing resin 622, a bonding wire 623, a wiring layer 624, and a substrate 625. The LED element 621 is provided on the substrate 625 and is connected to the wiring layer 624 via the bonding wire 623. The sealing resin 622 seals an inside of the substrate 625 with a resin so as to protect parts and connections in the substrate 625. The sealing resin 622 can contain phosphors so as to convert a luminescent color of the LED element 621. For example, the sealing resin 622 can configure, by use of a blue LED element and yellow phosphors, an LED package which emits a white color. Via the wiring layer 624, (i) parts connected via the solder 626 and (ii) a part in which the LED element 621 are wired.
According to an example illustrated in FIG. 17, the wiring layer 624 is configured to pass through the substrate 625. The solder 626 is connected to the wiring layer 624 on a bottom surface side of the substrate 625, and the LED element 621 is connected to the wiring layer 624 on a top surface side of the substrate 625.
With the arrangement illustrated in FIG. 17, the LED element 621 is mechanically fixed, while being electrically connected to the outside (not illustrated) via the wiring substrate 610, the connector 601, and the harness (not illustrated). This allows light emitting of the LED element 621 to be externally controlled.
FIG. 18 is a view illustrating another example of an LED light source substrate of a conventional edge-light type surface light source device. FIG. 19 is a cross-sectional view, taken on A-A line of FIG. 18, illustrating the LED light source substrate. An LED light source substrate 500, illustrated in each of FIGS. 18 and 19, is configured such that an LED element 515 is provided on a substrate 511 by use of a COB (Chip On Board) technique, instead of employing an LED package. That is, the LED element 515 is directly provided on the substrate 511. Alternatively, the substrate 511 can include another layer (e.g., a wiring layer 513) on a surface of the substrate 511. In this case, the LED element 515 can be provided on the another layer. In any case, in a case where the COB technique is employed, the LED element 515 is directly provided as it is, instead of being indirectly provided on a wiring substrate after being contained in a package.
The substrate 511 has a surface (a horizontal top surface of the substrate 511 illustrated in FIG. 19) and depressed parts recessed from the surface. Each LED element 515 is provided in a corresponding one of the depressed parts.
According to the LED light source substrate 500, the wiring layer 513 and the LED element 515 are electrically connected via a bonding wire 516. The wiring layer 513 is electrically connected to an electrode terminal of a connector 512 (not particularly illustrated). With the arrangement, it possible to control light emitted from the LED element 515, by electrically controlling the harness (not illustrated) connected to the connector 512.
The LED element 515, the bonding wire 516, and their connected parts are easily damaged by an impact. In order to prevent such a damage, the LED element 515 and the bonding wire 516, including their connected parts, are sealed with a sealing resin 514. That is, the sealing resin 514 is injected into each of the depressed parts. With the arrangement, the LED element 515 and the bonding wire 516 (i) are tolerable to a certain degree of externally applied impact and (ii) are protected from moisture, a foreign matter, and the like.
By adding a colorant and/or phosphors to the sealing resin 514, it is possible to adjust a color tone of light emitted from the LED light source substrate 500. For example, in a case where (i) the LED element 515 emits blue light or an ultraviolet ray and (ii) suitable phosphors are contained in the sealing resin 514, the LED light source substrate 500 can emit white light.
In a case where the LED light source substrate 140 is configured by use of an LED package and a wiring substrate, as with the LED light source substrate 600, at least the following advantages (1) and (2) are obtained: (1) since an outer shape of a substrate can be prepared by press processing or router processing, it is easy to prepare a substrate with a relatively large size; and (2) it is possible to mount an LED package by use of a general mounter. On the other hand, a method of providing an LED element by use of the COB technique, as with the LED light source substrate 500, has at least the following advantages (i) and (ii): (i) since no solder needs to be used when the LED element is mounted, there is no limitation of a temperature caused by a temperature of a solder in use; and (ii) since an LED light source substrate can be produced in a final form in a step similar to a step employed during producing of the LED package, a substrate can be produced at a low cost in a case where the substrate has a small size.
FIG. 20 is a view illustrating a reflection pattern of light observed in a case of a conventional edge-light type surface light source device. According to FIG. 20, light emitted from an LED light source substrate 140 enters a light guide plate 120 via an incident surface of the light guide plate 120 (a left side of the light guide plate 120 illustrated in FIG. 20). The light guide plate 120 is made up of a light guide body 121 and a reflection pattern 122.
According to FIG. 20, a typical trajectory of incident light is indicated by the arrows. Light, which is (i) emitted from the LED light source substrate 140 and then (ii) incident on the incident surface of the light guide body 121, travels as follows. That is, in a case where an incident angle of the incident light is less than a certain angle, such incident light is refracted and enters inside the light guide body 121. On the other hand, in a case where the incident angle is more than a certain angle, such an incident light is totally reflected from the incident surface and will never enter inside the light guide body 121.
The incident light, which has entered the light guide body 121, repeats a total reflection on a top surface and a bottom surface of the light guide body 121. In a case where the incident light reaches a reflection pattern 122, the incident light is diffused and reflected from the reflection pattern 122. This causes many components of the incident light to exit via the top surface, i.e., an emitting surface of the light guide body 121.
Normally, the reflection pattern 122 is properly set in order to (i) uniformize a surface light emitting pattern or (ii) realize a desired surface light emitting pattern. For example, in order to realize a uniform light emitting pattern, the reflection pattern 122 is set as follows. That is, the reflection pattern 122 is set so as to have a high density in a part far from a light source (e.g., (i) constituents of the reflection pattern are large, (ii) the number of the constituents per unit area is large, or (iii) a combination of the above (i) and (ii), etc.), whereas the reflection pattern is set so as to have a low density in a part near the light source (e.g., (a) constituents of the reflection pattern are small, (b) the number of the constituents per unit area is small, or (c) a combination of the above (a) and (b), etc.).
Examples of a material of the light guide body 121 encompass (i) an acrylic resin which has a very high transmittance, (ii) a polycarbonate which has (a) a certain degree of high transmittance and (b) a high strength. Particularly, the acrylic resin is often employed as a material of a surface light source module having a certain degree of large size. This is because an amount of light, which is lost due to light absorption by the light guide plate, cannot be ignored. On the other hand, the polycarbonate is often employed as a material of a surface light source module which is in a relatively small size and needs a strength.
The reflection pattern 122 can be added to the light guide body 121 by carrying out laser marking with respect to the light guide body 121, applying a paint to the light guide body 121, or the like. Alternatively, the reflection pattern 122 can be realized in a shape which is simultaneously formed when the light guide body 121 is formed.
The following description will discuss, with reference to FIGS. 21 through 24, an arrangement of a light source substrate of a conventional edge-light type surface light source device. FIG. 21 through are each a view schematically illustrating an arrangement(s) of a light source substrate(s) of a conventional edge-light type surface light source device.
According to an example illustrated in FIG. 21, a light source substrate 140a and a light source substrate 140b are arranged on a respective pair of long sides of the light guide plate 120 (an upper side and a lower side of the light guide plate 120 illustrated in FIG. 21). The light source substrate 140a and the light source substrate 140b have lengths equal to those of the respective pair of long sides of the light guide plate 120.
According to an example illustrated in FIG. 22, a light source substrate 140a and a light source substrate 140b are arranged on a respective pair of short sides of the light guide plate 120 (a left side and a right side of the light guide plate 120 illustrated in FIG. 22). The light source substrate 140a and the light source substrate 140b have lengths equal to those of the respective pair of short sides of the light guide plate 120.
According to an example illustrated in FIG. 23, a light source substrate 140 is arranged on a long side of a light guide plate 120 (a lower side of the light guide plate 120 illustrated in FIG. 23). The light source substrate 140 has a length equal to that of the long side of the light guide plate 120.
According to an example illustrated in FIG. 24, a light source substrate 140 is arranged on a short side of a light guide plate 120 (a left side of the light guide plate 120 illustrated in FIG. 24). The light source substrate 140 has a length equal to that of the short side of the light guide plate 120.
Note here that a total length of a light source substrate can be made shorter in a case where the light source substrate is arranged on a short side of a light guide plate, as compared with a case where the light source substrate is arranged on a long side of the light guide plate. The total length of the light source substrate can be made shorter in a case where the light source substrate is arranged on one (1) side of the light guide plate, as compared with a case where light source substrates are arranged on respective two sides of the light guide plate.
For example, a total length of a light source substrate can be made shorter in the arrangement illustrated in FIG. 22, as compared with the arrangement illustrated in FIG. 21. The total length of the light source substrate can be made shorter in the arrangement illustrated in FIG. 23, as compared with the arrangement illustrated in FIG. 21. The total length of the light source substrate can be made shorter in the arrangement illustrated in FIG. 24, as compared with the arrangement illustrated in FIG. 22.
Generally, shortening a total length of a light source substrate brings about many advantages. Examples of such advantages encompass (i) a reduction in production cost, (ii) a reduction in product weight, (iii) a reduction in burden on the environment due to a reduction in amount of a material to be used, and (iv) a reduction in a transportation cost due to a reduction in size and weight of a product.
Note, however, that even in a case where the arrangement illustrated in FIG. 24 is employed which can make shortest the total length of the light source substrate, the light source substrate needs to have lengths each equal to that of a corresponding side of the light guide plate. This is because it is necessary to meet a demand for uniformizing a luminance in the light guide plate as much as possible. Such a demand can be easily met in a case where the light source substrate has lengths each equal to that of a corresponding side of the light guide plate. For example, in a case where (i) the arrangement illustrated in FIG. 24 is employed and (ii) the light source substrate has a length shorter than that of a corresponding side of the light guide plate, a problem arises that a sufficient luminance cannot be obtained in a part of the light guide plate.
The following description will specifically discuss such a problem with reference to FIG. 25. FIG. 25 is a view illustrating a range which is irradiated with light emitted from a light source substrate of a conventional surface light source device in which the light source substrate is arranged on a side of a light guide plate. FIG. 25 illustrates an example in which the conventional surface light source device is configured such that a light source substrate 140 which has a length shorter than that of a short side of a light guide plate 120 is tentatively arranged on the short side of the light guide plate 120.
According to the conventional surface light source device, light emitted from the LED light source substrate 140 travels in a right side direction of the light guide plate 120. A range 210a which is irradiated with the light has (i) a spread which is at a refraction angle α with a direction where an upper side of the light guide plate 120 extends and (ii) a spread which is at a refraction angle α with a direction where a lower side of the light guide plate 120 extends (see FIG. 25).
This is because the light emitted from the LED light source substrate 140 is refracted when it goes through a side surface (i.e., a boundary surface) of the light guide plate 120. This causes dark parts (unhatched parts illustrated in FIG. 25), which are not irradiated with light emitted from the LED light source substrate 140, to be formed in respective of an upper left corner part and an lower left corner part of the light guide plate 120 (see FIG. 25).
As described above, in a case where the light source substrate 140 has a length shorter than that of a corresponding side of the light guide plate 120, the range 210a can be directly irradiated with light, while the dark parts cannot be directly irradiated with light. This prevents the light guide plate of the conventional surface light source device from obtaining a sufficient luminance. Accordingly, the light source substrate 140 cannot have a length shorter than that of a corresponding short side of the light guide plate 120.
It is true that, in a case where the length of the long side of the light guide plate 120 is extended, instead of shortening the length of the light source substrate 140, an entire range of the light guide plate 120 in an original size can be a range which is irradiated with light. Note, however, that a length of an extended part of the long side of the light guide plate 120 cannot normally exceed ten percent of the length of the short side of the light guide plate 120.
For example, in a case where the light guide plate 120 is made of an acrylic resin (a refractive index: 1.49), a critical angle α is approximately 42 degrees. Some optical glasses each have a refractive index of approximately 1.43, which is lower than that of the acrylic resin. In this case where the light guide plate 120 is made of such an optical glass, a critical angle α is approximately 45 degrees. In this case, if the light source substrate 140 has a length less than 0.8 times of a length of a corresponding short side of the light guide plate 120, a length of the extended part of the long side of the light guide plate 120 exceeds ten percent of the length of the corresponding short side of the light guide plate 120. Accordingly, it is very difficult that the light source substrate 140 has a length not more than 0.8 times of the length of the corresponding short side of the light guide plate 120.
Having said that, a demand remains unchanged for realizing an arrangement in which a light source substrate has a length shorter than that of a corresponding side of a light guide plate. In view of the circumstances, in order to meet such a demand, a technique has been devised in which a light source substrate has a length shorter than that of a corresponding side of a light guide plate.
For example, Patent Literature 2 discloses an arrangement in which (i) a light source has a length shorter than that of a short side of a light guide plate and (ii) an illumination light introducing section is provided so that illumination light emitted from the light source is spread so as to be introduced to the light guide plate.
Patent Literature 3 discloses an arrangement in which (i) a light source has a length shorter than that of a short side of a light guide plate and (ii) the light guide plate has a light scattering hole so that light is diffused in the light guide plate.
Patent Literatures 4 and 5 each disclose an arrangement in which a light source having an L shape is arranged in a corner part of a light guide plate so as to uniformize a display luminance, while reducing power consumption of the light source.